1. Field of the Invention
The present invention relates to a structure of a piping with a coolant inlet.
2. Description of the Background Art
In recent years, in a hybrid vehicle and the like, an economy running system (also called an idling stop system and the like) has been developed, which automatically stops an engine when the vehicle stops at an intersection, and restarts the engine upon an operation by a driver to restart the vehicle.
In this system, it is necessary to supply power to auxiliary machinery (an air conditioner, a headlight, an audio system, and so on) and to a motor generator operative to restart an engine. Accordingly, two power sources having different voltages (a 12V battery, a 36V battery and a 200V battery or more etc.) and a PCU (Power Control Unit) including an inverter and a converter are mounted. The PCU is connected to these two power sources and also to the motor generator installed on the side of the engine via a power cable.
The PCU is cooled down by a coolant in order to prevent an increase in temperature caused by an electric circuit therewithin. This coolant for the PCU provides a cooling system having a coolant circulation path in which heat exchange with the outside air is performed by an electric water pump and a radiator, which system is provided separately from the coolant for the engine.
Not only in the cooling system employed in the above-described PCU, but also in the above-described cooling system generally using a coolant, a piping with a coolant inlet is provided in the circulation path as a region for storing the coolant and to be replenished with it periodically. This piping with the coolant inlet that is in the shape of a tank enabling a temporary accumulation of the coolant is provided with a feed port for feeding the coolant in the tank to the coolant circulation path, a return port for returning the coolant circulated through the coolant circulation path into the tank, and an inlet for injecting the coolant into the tank. One example of the coolant circulation path using such piping with the coolant inlet is disclosed in Japanese Patent Laying-Open No. 2004-082921.
In the coolant circulation path using the piping with the coolant inlet having the above-described configuration, however, there is a problem of air mixed into or generated in the path when the electrical water pump is used to circulate the coolant. In particular, in a vehicle and the like, space for placing the coolant circulation path is often limited. Thus, with the water pump capacity maintained, the coolant circulation path and the piping with the coolant inlet are reduced in size, and as a result, the coolant circulation path becomes complicated. This tends to increase the possibility of mixing the air into the coolant circulation path.
The mixing of the air into the cooling path causes problems such as unusual noise in the water pump, a decrease in durability of the water pump, and shortening of intervals between operation cycles for removing the air in the cooling path. Furthermore, it is also suggested that the coolant circulation path is completely sealed so as to avoid the mixing of the air. However, in this case, it is known that the piping with the coolant inlet should be increased in size, which goes against the need for reducing the size of the piping with the coolant inlet. In addition, it is also difficult to consider modifications to the coolant circulation path in the light of the arrangement of other equipment.